Smoke rises from the front line of a clash south of Kirkuk, Iraq, on Saturday, March 14.

Hide Caption

3 of 52

The ISIS terror threat52 photos

A group of Kurdish Peshmerga troops take a break from fighting ISIS militants south of Kirkuk on March 14.

Hide Caption

4 of 52

The ISIS terror threat52 photos

Iraqi security forces and allied Shiite militiamen gather in Tikrit on Friday, March 13. Ousting ISIS from Tikrit is important for the United States-led coalition trying to thwart the extremist group's quest to grow its caliphate. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.

Hide Caption

5 of 52

The ISIS terror threat52 photos

A motorcyclist passes destroyed buildings in the Syrian town of Kobani on Thursday, March 12, after it has been freed from ISIS militants.

Hide Caption

6 of 52

The ISIS terror threat52 photos

Smoke billows after a mortar shell hit an Anbar governorate building in Ramadi, Iraq, on Wednesday, March 11. ISIS has launched a coordinated attack on government-held areas of the western Iraqi city. Ramadi has been the focus of a fierce ISIS assault since Iraqi forces made gains against the group in Tikrit.

Hide Caption

7 of 52

The ISIS terror threat52 photos

The parents of 19-year-old Mohammed Musallam react at the family's home in the East Jerusalem Jewish settlement of Neve Yaakov on Tuesday, March 10. ISIS released a video purportedly showing a young boy executing Musallam, an Israeli citizen of Palestinian descent who ISIS claimed infiltrated the group in Syria to spy for the Jewish state. Musallam's family told CNN that he had no ties with the Mossad, Israel's spy agency, and had, in fact, been recruited by ISIS.

Hide Caption

8 of 52

The ISIS terror threat52 photos

Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.

Hide Caption

9 of 52

The ISIS terror threat52 photos

Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants recently abducted at least 220 Assyrians in Syria.

Hide Caption

10 of 52

The ISIS terror threat52 photos

Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

Hide Caption

11 of 52

The ISIS terror threat52 photos

A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.

Hide Caption

12 of 52

The ISIS terror threat52 photos

Smoke billows in Kirkuk as Kurdish Peshmerga fighters take position against ISIS militants on January 30.

Hide Caption

13 of 52

The ISIS terror threat52 photos

Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.

Hide Caption

14 of 52

The ISIS terror threat52 photos

Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.

Hide Caption

15 of 52

The ISIS terror threat52 photos

Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.

Hide Caption

16 of 52

The ISIS terror threat52 photos

ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.

Hide Caption

17 of 52

The ISIS terror threat52 photos

An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.

Hide Caption

18 of 52

The ISIS terror threat52 photos

Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.

Hide Caption

19 of 52

The ISIS terror threat52 photos

Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.

Hide Caption

20 of 52

The ISIS terror threat52 photos

A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.

Hide Caption

21 of 52

The ISIS terror threat52 photos

Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.

Hide Caption

22 of 52

The ISIS terror threat52 photos

ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.

Hide Caption

23 of 52

The ISIS terror threat52 photos

A U.S. Air Force plane flies above Kobani on Saturday, October 18.

Hide Caption

24 of 52

The ISIS terror threat52 photos

Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.

Hide Caption

25 of 52

The ISIS terror threat52 photos

Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.

Hide Caption

26 of 52

The ISIS terror threat52 photos

Turkish police officers secure a basketball stadium in Suruc on October 14. Some Syrian Kurds were held there after crossing from Syria into Turkey. Tens of thousands of people fled Kobani to escape ISIS.

Hide Caption

27 of 52

The ISIS terror threat52 photos

Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.

Hide Caption

28 of 52

The ISIS terror threat52 photos

Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.

Hide Caption

29 of 52

The ISIS terror threat52 photos

In this photo released by the U.S. Air Force on Saturday, October 4, a U.S. Navy jet is refueled in Iraqi airspace after conducting an airstrike against ISIS militants.

Hide Caption

30 of 52

The ISIS terror threat52 photos

A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.

Hide Caption

31 of 52

The ISIS terror threat52 photos

Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.

Hide Caption

32 of 52

The ISIS terror threat52 photos

Tomahawk missiles, intended for ISIS targets in Syria, fly above the Persian Gulf after being fired by the USS Philippine Sea in this image released by the U.S. Navy on Tuesday, September 23.

Hide Caption

33 of 52

The ISIS terror threat52 photos

Turkish Kurds clash with Turkish security forces during a protest near Suruc on Monday, September 22. According to Time magazine, the protests were over Turkey's temporary decision to close the border with Syria.

Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.

Hide Caption

38 of 52

The ISIS terror threat52 photos

Iraqi volunteer fighters celebrate breaking the Amerli siege on Monday, September 1. ISIS militants had surrounded Amerli, 70 miles north of Baquba, Iraq, since mid-June.

Hide Caption

39 of 52

The ISIS terror threat52 photos

Kurdish Peshmergas fight to regain control of the town of Celavle, in Iraq's Diyala province, on August 24.

Hide Caption

40 of 52

The ISIS terror threat52 photos

Peshmerga fighters stand guard at Mosul Dam in northern Iraq on Thursday, August 21. With the help of U.S. military airstrikes, Kurdish and Iraqi forces retook the dam from ISIS militants on August 18. A breach of the dam would have been catastrophic for millions of Iraqis who live downstream from it.

Hide Caption

41 of 52

The ISIS terror threat52 photos

Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.

Hide Caption

42 of 52

The ISIS terror threat52 photos

Peshmerga fighters inspect the remains of a car that reportedly belonged to ISIS militants and was targeted by a U.S. airstrike in the village of Baqufa, north of Mosul, on August 18.

Hide Caption

43 of 52

The ISIS terror threat52 photos

Kurdish Peshmerga fighters fire at ISIS in Khazair, Iraq, on Thursday, August 14.

Hide Caption

44 of 52

The ISIS terror threat52 photos

Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

Hide Caption

45 of 52

The ISIS terror threat52 photos

Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.

Hide Caption

46 of 52

The ISIS terror threat52 photos

A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.

Hide Caption

47 of 52

The ISIS terror threat52 photos

A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.

Hide Caption

48 of 52

The ISIS terror threat52 photos

New army recruits gather in Najaf, Iraq, on Wednesday, June 18, following a call for Iraqis to take up arms against Islamic militant fighters.

Hide Caption

49 of 52

The ISIS terror threat52 photos

Kurdish Peshmerga forces, along with Iraqi special forces, deploy their troops and armored vehicles outside of Kirkuk, Iraq, on June 12.

Hide Caption

50 of 52

The ISIS terror threat52 photos

Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.

Hide Caption

51 of 52

The ISIS terror threat52 photos

Civilians from Mosul escape to a refugee camp near Irbil, Iraq, on June 10.

Hide Caption

52 of 52

Story highlights

ISIS' "ability to continually shape and control the conflict will be sorely tested," analyst says

Its success so far is largely due to the weakness of its opponents, analysts say

For now, observers say ISIS still has momentum, but opponents can turn the tide

Surprise, mobility and the merciless treatment of opponents: the blueprint of the Islamic State in Syria and Iraq as it has gobbled up territory in both Syria and Iraq over the past few months. But as its adversaries regroup, ISIS -- which now calls itself the Islamic State -- may begin to suffer setbacks on the battlefield, according to a new analysis of its capabilities and tactics.

"As a defensive force, the ISIS may struggle to hold terrain if it is attacked simultaneously at multiple points or if its auxiliary allies begin to defect," says Michael Knights, who has worked throughout Iraq and is now a fellow at The Washington Institute for Near East Policy.

Knights says ISIS has a deep bench of talented military planners, veterans of the Iraq insurgency during the U.S. occupation and of the group's creation of a mini-state in Syria. It has foreign jihadists who have fought in Chechnya and the Balkans. "Yet the pace of the war against the ISIL is accelerating, and the group's ability to continually shape and control the conflict will be sorely tested," Knights writes in the latest edition of Sentinel, published by the Combating Terrorism Center at West Point.

Military analysts say ISIS' success so far is largely due to the weakness of its opponents, as well as years of meticulous planning after Abu Bakr al-Baghdadi's "reboot" of the group in 2010.

Just Watched

New clues in James Foley execution video

This war of attrition included a campaign to intimidate and assassinate senior members of the Iraqi security forces last year, a campaign al-Baghdadi called the "Soldiers' Harvest." Al-Baghdadi built a command structure designed to combine centralized control with execution at the local level. This was highly successful during 2012-13 when the group synchronized waves of car bombings in different locations across Iraq. It was in evidence at the weekend in Kurdish-controlled Kirkuk, when a series of three car bombs and a roadside bomb killed at least 20 people.

ISIS has weaved this tactic into its current military campaign. Earlier this month, a well-planned attack against the Kurdish town of Jalula began with a suicide car bomb that killed more than 20 Peshmerga, "a second tanker truck suicide device in the town center, followed by individual suicide-vest bombings on 12 checkpoints by fighters wearing Kurdish-style uniforms," Knights says.

These multiple suicide bombings instil fear and panic in civilians and military opponents alike. They are ISIS' "shock and awe" tactic, complemented by the agility and speed of ISIS units. "The relative compactness of Iraq, where good roads allow large swathes of the country to be traversed in a single day, gives an aggressive force strong ability to concentrate forces at a given point of attack," says Knights.

There have been claims that ISIS is using U.S.-made M-1 Abrams tanks and Humvees seized from the Iraqi army. And sometimes heavy armor has made an important difference. ISIS used a single Iraqi T-55 tank of Soviet vintage earlier this month to fend off an attempt to break the siege of Amerli. But pinpoint U.S. airstrikes have already changed the local balance around the Mosul Dam and Sinjar.

Knights told CNN: "Though ISIS have undoubtedly captured 200-300 Humvees and will be able to keep them operational for many months before they require spare parts, other U.S.-provided vehicles are present in very limited amounts. In part this is because they are complex to operate and maintain. Very few were captured in good working order because the Iraqis themselves were having trouble keeping them running."

Knights says that there is no evidence that ISIS fighters have been able to operate M-1 Abrams -- nor U.S. manufactured 155mm howitzers. It does have far more armored trucks with heavy machine guns than it did before June, allowing it to overrun lightly armed checkpoints. "But faced with U.S. airpower or even the slowly recovering Iraqi and Kurdish security forces, such vehicles become death traps," says Knights, citing the group's losses at the Mosul Dam.

Making resistance appear hopeless to potential opponents is a critical part of ISIS' strategy. A tribal revolt in Zowiya in Salahuddin province last month was met with sustained mortar fire that almost razed the town. Those who wanted to re-enter Zowiya had to "repent."

"If local populations cannot mount an effective resistance to ISIS, then they likely will not attempt to do so," says Jessica Lewis at the Institute for the Study of War.

ISIS may have as few as 15,000 fighters for a vast area stretching from northern Syria to the middle of Iraq. So deception is also critical to its success. On many occasions it has appeared to be launching an attack -- drawing defending forces toward it -- only to strike the place those forces have left. Earlier this month, ISIS hit Jalula, after Peshmerga had left the town to confront an ISIS thrust at Makhmour.

Will Obama hit ISIS in Syria?

Just Watched

Syria: We'll collaborate to defeat ISIS

The fact that it has relatively few fighters per square mile may explain why it prefers to depopulate some towns because of an "accentuated fear of local uprisings and informers," says Knights. That could be a double-edged sword, because living among civilians in densely populated places should offer the group some protection. But there is evidence that the Iraqi air force strikes even when civilians are present. "My sense from talking to people along the ISIS front line is that the group welcomes being able to shuffle discretely around depopulated towns," says Knights.

And airstrikes, unless limited and carefully targeted, might even end up helping ISIS. "Airstrikes into the Sunni heartland of Iraq or Syria may exacerbate the sectarian conflict in the region by illustrating a passive or active alignment of the U.S. with Iran in order to bring firepower to bear against Sunnis," says Lewis.

ISIS has also traded on tribal rivalries to consolidate its position, "such as by plugging into the anti-Kurdish sentiments of Arab tribes around Jalula or allowing Arab tribes to harvest the ripe wheat fields of displaced Shi`a Turkmen farmers at Amerli," says Knights.

These local arrangements may work for a time, but ISIS is likely to encounter stiffer opposition. Its use of surprise will be slowly devalued, as its tactics are studied -- and especially as the Iraqi Security Forces and Kurdish Peshmerga begin to receive a flow of real-time intelligence from the U.S. surveillance. Knights says he was told by Kurdish sources that ISIS tried to infiltrate the town of Tuz Khurmatu after dark two weeks ago. But its fighters were detected by the U.S. military, which provided Kurdish artillery with the coordinates required to blunt the attacks.

Knights told CNN that "U.S. special forces seem to be operating along the front line, visually checking and designating targets. U.S. headquarters personnel at the joint operations center in Irbil [the capital of Iraqi Kurdistan] are helping the Kurds and the [Iraqi] air force to coordinate their actions and to avoid 'friendly fire'."

And then there is the weight of expectation among ISIS supporters. Its momentum has helped swell its ranks as both foreign fighters and young radicalized Iraqi Sunnis have flocked to join. But al-Baghdadi's declaration of a Caliphate means ISIS has to "demonstrate that its physical stronghold is defensible, or at least prevent rival militaries from attacking it," says Lewis.

ISIS has shown a rudimentary ability to defend its gains, building berms, booby-trapping approach roads and destroying bridges. It has successfully ambushed Iraqi troops and Shia militia trying to retake Tikrit. But defensive positions and predictable counterattacks leave its forces more exposed to airstrikes.

"ISIS' defensive style has two components," Knights told CNN. "They use roadside bombs and vehicle-carried remotely detonated bombs to create explosive emplacement hazards along key routes and in key towns. The U.S. has shown that, along with ground sources, it can remotely spot and destroy these from the air."

"ISIS' other key preference is for counterattacks, almost as an instinctive reaction to losing ground. This is an organization that much prefers to be on the attack, even tactically, as part of a defensive operation. But counterattacking ISIS convoys are easy meat for U.S. airpower and even for Iraqi aviators," he adds.

And if ISIS has to do more defending than attacking -- as seems likely -- the Sunni communities that have supported, accepted or acquiesced to it may think twice.

"If the ISF and Kurdish forces undertake selective offensive operations on a widening number of battlefields," Knights says, ISIS and its allies "will undoubtedly become stretched, particularly if its ability to move and mass counterattacking forces is limited."

Another vulnerability may be lines of communication between Raqqa in Syria, ISIS' administrative headquarters, and its units in Iraq. "Snapping the ISIS caliphate in half is a key objective, both to undermine the narrative of a transnational caliphate that can be defended, and to reduce the synergies of two insurgencies fighting back-to-back," Knights told CNN.

For now, observers say ISIS still has momentum, and repeatedly demonstrates its ability to fight on many fronts simultaneously, pacify or co-opt towns and villages that might otherwise resist and hold territory against the Iraqi Security Forces, which have been weakened by several years of political interference and poor leadership. The idea that the ISF are capable of retaking Mosul anytime soon seems far-fetched.

Better co-ordination among its opponents, and the psychological effect of going on the defensive, may begin to turn the tide. But to borrow a phrase from another conflict, most analysts believe we are not close to the beginning of the end in the battle against ISIS, rather anticipating the end of the beginning.